Modern modems operating on low voltage power grids use multi-carrier modulation (“MCM”) techniques. These modems transmit information in symbols spread out sequentially in time and across different frequency carriers. While each individual frequency carriers may occupy a narrow bandwidth, the composite signal of the individual frequency carriers forms a broad bandwidth. Standards such as IEEE P1901.2 and ITU 9953 (G3) specify orthogonal frequency-division multiplexing (“OFDM”) as the modulation technique for power grid communications. One characteristic inherent with signal transmission over a power grid is the concentration of signal errors (i.e., noise bursts) that seems to occur in certain time and/or frequency windows. When the concentration of signal errors in a contiguous region of a signal transmission is too high, the error correction techniques applied to the signal transmission, such as the use of convolutional error code, tend to perform poorly.